Is this... is this a serious question that's seriously being asked in a serious manner?
If climate change truly gets as bad as some predict, the US will lose a lot of farmland and sources of freshwater, while Canada will still be thinly-populated, abundant with resources, and an improving climate.
If climate change truly gets as bad as some predict, why on earth wouldn't the US apply pressure to force Canada into a union with the US and then annexation? It would be within our vital national security and economic interests.
Because it's a stupid, self-centered proposition to act as if we're just entitled to go about annexing our closest ally who also happens to be the world's second largest country; because it'll never legitimately get as far as annexation (
maybe a union, but not outright annexation); & because we're neither as hegemonic as we like to think we are or as the world likes to claim we are?